SSALTO/DUACS: THREE-SATELLITE QUALITY LEVEL RESTORED IN NEAR REAL TIME

sleepyeyeegyptianΠετρελαϊκά και Εξόρυξη

8 Νοε 2013 (πριν από 4 χρόνια και 5 μέρες)

101 εμφανίσεις

SSALTO/DUACS: THREE
-
SATELLITE QUALITY LE
VEL RESTORED IN
NEAR REAL TIME


M
-
I;Pujol
1
, G. Dibarboure
1
,
E.
B
r
on
ner
2


1
CLS, Space Oceanography Division, Toulouse, France

2
CNES, Toulouse, France



1
-

Project Overview

Objective
s


To pr
ovide operational applicati
ons
with homogeneous and directly usable high quality altimeter
data from all missions (Jason
-
1, Jason
-
2, T/P, ENVISAT, GFO, ERS1/2 and even GEOSAT). The
system uses common processing facilities for global and regional applications. It ensures that
upgrade
s are consistently applied on all products to better serve the altimetry user community.


Near Real Time (NRT): Daily Operational Products

DUACS
-
NRT provides GODAE, climate forecasting centers, the MyOcean EU FP7 project, and real time
oceanographic resear
ch (e.g.: in
-
situ campaigns) with directly usable, high quality near real time altimeter
data. Regional products (European Shelves, Mediterranean Sea, and Black Sea) are delivered to operational
projects. Commercial applications are also developed for the
fishery and offshore drilling industries. All
DUACS near real time products are generated and distributed on a daily basis to reduce the NRT delay, and
to smooth the operational procedures of NRT users.

DUACS features a systematic quality control of the in
put data, the system itself, and its products with
detailed reports put online twice per week. The system also carries out on
-
the
-
fly editing and reprocessing of
erroneous datasets, as well as a long term monitoring of NRT data it has used, to quickly dete
ct anomalies,
drifts and discontinuities in incoming altimeter data.


Delayed Time (DT): A consistent data set built upon all altimeters

The second generation of DUACS
-
DT products is composed of global data sets of along track and gridded
Sea Level Anomaly
, Absolute Dynamic Topography, and geostrophic currents, but also of regional
-
specific
products (higher resolution, optimized parameters). DUACS reprocessed all past altimeter data: Jason
-
1, T/P,
ENVISAT, GFO, ERS1/2 and GEOSAT. These delayed time products

are regularly updated when new
Level2 data are released and fully validated. The system operationally integrates the state
-
of
-
the
-
art
corrections, models and references recommended by the altimeter community, as well as the best Cal/Val and
cross
-
calibrat
ion and merging algorithms.

A complete reprocessed DUACS DT data set will be available on next spring (see §3).




2
-

Operatio
nal Jason tandem
products only 10 days after orbit change

The DUACS system was significantly modified to integrate Jason
-
2. Afte
r a successful experimental phase
during the temporary absence of Jason
-
1 in August 2008, Jason
-
2 definitively became the reference mission
of the system
on

January 21, 2009,

a

few days before Jason
-
1
was

moved on its new orbit.
Data from t
he
latter

were r
e
-
integrated in

DUACS
in

Mar
ch

2009.
Thanks to the excellent consistency of the Jason tandem
data, this upgrade was made

operational
only 10 days after Jason
-
1 reached its
interleaved

orbit.

The
performances of the
multi
-
satellite
system were greatly impro
ved with the
combination of
Jason
-
2

and
Jason
-
1. The tandem allowed a reduction of the formal mapping error from 20 to 60% of the variance of the signal
,

assuring an improved restitution of mesoscale structures especially in high energetic areas

where the
mean
gain in EKE is ~45%
.
This increase can locally reach more than 75%
(
Figure
1
).


Moreover, with NRT processing, SLA observed with the Jason tandem shows a temporal coherency s
trongly
improved in comparison
to h
istorical Jason
-
1/Topex tandem. Actually, the 10
-
day repetitivity of each of the
satellite affects the signal restitution with an
artificial 10
-
day cycle. It is
strongly reduced thanks to the
temporal shift between Jason
-
1 and Jason
-
2 satellites
(
Figure
2
).




Figure
1
:
Mean EKE over a 4 months period
(Jason2 vs Tandem maps)



a)
b)

Figure
2
: Mean EKE (cm²/s²) on a 500km wide zone. a) Jason1 vs Jason1/Topex
-
Poseid
on tandem; b) Jason2 vs
Jason2/Jason1 tandem.



3
-

Ongoing Improvements to secure multi
-
mission products

The
DUACS system
’s

accurac
y and resilience (e.g.
against data gaps or temporary delay) depend on
the
number of altimeter data

flows

available.
Moreove
r, l
ower quality measurements (orbit determination)
combined with non
-
centered processing time
-
windows make the NRT processing more sensitive to the
number of altimeter missions involved in the system. If two altimeters are acknowledged as the bare
minimum

needed to observe mesoscale signals in DT (offline) maps, three or even four missions are needed
to obtain equivalent accuracy in NRT (Pascual & al., 2008).

T
he
recent introduction of Jason
-
2/Jason
-
1 tandem

increased the resilience and precision of the sy
stem. A
better restitution of ocean variability is observed, especially in high energetic areas (Fig. 1).

Moreover,
integration of OGDR/FDGDR
Jason
-
2, Jason
-
1 and Envisat

data
in the NRT system also largely contribute
to the improved resilience and precisi
on of the system.

Additional DUACS upgrades are also being worked on:
Cryosat is scheduled
for launch in
late

2009.
Initially aimed at ice observation, the mission may provide opportunity data on ocean as well. System and
algorithm upgrades are being worke
d on to use this additional dataset in the multi
-
satellite system by mid
-
2010 (pending green light from the CalVal phase).

Similarly, an
important orbit change is scheduled for
ENVISAT

by mid
-
2010. The resulting drifting ground track will significantly aff
ect DUACS processing and
ERS2 data will no longer be redundant with ENVISAT’s. A
re
-
integration of ERS2 in DUACS

is envisaged
by mid
-
2010.

I
n order to minimize the impact of an anomaly on the reference mission used in DUACS (especially in NRT),
a new orbit

error reduction scheme

based on multiple reference missions (e.g.: Jason
-
2 and Jason1, or
Jason
-
2 and AltiKa/Saral) is being developed.
It will
take advantage of the improved POD with existing and
future mission, since no mission brows the
a
bsolute truth.

Lastly, DUACS is currently performing a
complete reprocessing of all altimetric time series

(1992
-
2009, 7
sensors, for a cumulated dataset of more than 50 years) with the most recent standards recommended by the
altimetry community (e.g. GDR
-
C or equivale
nt algorithms, GFSC orbits and new SSB on GFO…), as well
as various processing upgrades from recent CNES projects (e.g. PISTACH, SLOOP). The next generation of
global and regional products from DUACS will be available next spring.